1. Field of the Invention
The invention relates to a fuel supply apparatus and a fuel supply method of an internal combustion engine.
2. Description of the Related Art
Japanese Patent Application Publication No. 2000-008997 (hereinafter referred to as “JP-A-2000-008997”) describes a fuel supply apparatus that is driven by an internal combustion engine. More specifically, this apparatus is provided with a high-pressure pump having a plunger that is supported so as to move up and down in a cylinder. Because the plunger is driven up and down by a cam formed on a camshaft, fuel is drawn up into a pressurizing chamber, and the fuel is pressurized by the plunger and pumped into a delivery pipe. This delivery pipe is connected to injectors corresponding to each cylinder. Fuel is injected from these injectors into a combustion chamber in each cylinder.
Also, in JP-A-2000-008997, an electromagnetic valve which functions as a fuel delivery amount adjusting mechanism is provided in the high-pressure pump. This electromagnetic valve adjusts the fuel delivery amount from the high-pressure pump based on the operating state of the internal combustion engine (hereinafter simply referred to as “engine operating state”). Incidentally, the high-pressure pump is drivingly connected to an output shaft of the internal combustion engine (hereinafter simply referred to as “engine output shaft”). Therefore, the range within which this electromagnetic valve may adjust the fuel delivery amount changes according to the rotation speed of the engine output shaft.
If an abnormality such as a driving disability occurs with the electromagnetic valve in the high-pressure pump, the fuel delivery amount will no longer be adjusted in the manner described above. In this case, an excessive amount of fuel may be supplied from the high-pressure pump to a fuel line such as the delivery pipe, causing the fuel pressure in the fuel line to increase unnecessarily. Therefore, in this kind of fuel supply apparatus, a relief valve is usually provided in the delivery pipe or the like such that if the fuel pressure in the fuel line reaches or exceeds a relief pressure of the relief valve, fuel will be flow out of the fuel line through the relief valve, thereby reducing the fuel pressure in the fuel line.
However, there is a limit as to just how much the fuel pressure may be reduced by allowing fuel to flow out of the fuel line via the relief valve in this way. Also, if the amount of fuel supplied from the high-pressure pump increases, the fuel pressure in the fuel line becomes extremely high, which may result in fuel leaking from the fuel injector into the combustion chamber in the engine, for example.
Incidentally, problems such as the fuel pressure in the fuel line increasing excessively and fuel leaking from the fuel injection device into the combustion chamber, are not limited to a fuel supply apparatus that employs a plunger type high-pressure pump. These problems may also occur in a fuel supply apparatus that employs another fuel delivery device that is drivingly connected to the engine output shaft.